<template>
  <div>
    <router-link
      tag="div"
      to="/"
      class="header-abs"
      v-show="showAbs"
    >
      <div class="header-abs-back iconfont">&#xe602;</div>
    </router-link>
    <div
      class="header-fixed"
      v-show="!showAbs"
      :style="opacityStyle"
    >
      <router-link to="/">
        <div class="iconfont header-fixed-back">&#xe602;</div>
      </router-link>
      景点详情
    </div>
  </div>
</template>

<script>
  export default {
    name: "detail-header",
    data(){
      return{
        showAbs: true,
        opacityStyle: {
          opacity: 0
        }
      }
    },
    /*activated () {
      //为window对象添加一个事件监听处理，当发生窗体滚动事件时，触发handleScroll方法
      window.addEventListener('scroll', this.handleScroll)
    },
    deactivated(){//与activated相对，当页面被隐藏是调用，要记得解绑全局事件
      window.removeEventListener('scroll', this.handleScroll);
    },*/
    mounted () {
      //为window对象添加一个事件监听处理，当发生窗体滚动事件时，触发handleScroll方法
      window.addEventListener('scroll', this.handleScroll)
    },
    destroyed(){//与activated相对，当页面被隐藏是调用，要记得解绑全局事件
      console.log('移除事件绑定');
      window.removeEventListener('scroll', this.handleScroll);
    },
    methods:{
      handleScroll () {
        const top = document.documentElement.scrollTop//获取文档滚动的高度（相对于初始状态）
        if (top > 60) {//圆圈看不见时
          let opacity = top / 140//计算不透明度的值
          opacity = opacity > 1 ? 1 : opacity
          this.opacityStyle = { opacity }
          this.showAbs = false//让header-fixed显示出来
        } else {
          this.showAbs = true
        }
      }
    }
  }
</script>

<style lang="stylus" scoped>
  @import "~styles/variable.styl"
  .header-abs
    position: absolute
    left: .2rem
    top: .2rem
    width: .8rem
    height: .8rem
    line-height: .8rem /*使标致在圆中心*/
    border-radius: .4rem /*画一个圆*/
    text-align: center /*使标致在圆中心*/
    background: rgba(0, 0, 0, .8)
    .header-abs-back
      color: #fff
      font-size: .4rem

  .header-fixed
    z-index 2
    position: fixed
    top: 0
    left: 0
    right: 0
    height: $header-height
    line-height: $header-height
    text-align: center
    color: #fff
    background: $bgColor
    font-size: .32rem
    .header-fixed-back
      position: absolute
      top: 0
      left: 0
      width: .64rem
      text-align: center
      font-size: .4rem
      color: #fff
</style>
